Nitrogen is one of the most important industrial gases in the world, second only to oxygen in use. At the present time, nitrogen is generally delivered to the user as substantially pure nitrogen in bulk liquid form. A method that is currently most frequently used for the production of such substantially pure nitrogen is by air liquefaction and fractionation. While this method has the advantage of also simultaneously resulting in the production of high-purity oxygen, it nevertheless has the pronounced disadvantage that it is expensive to perform and energy intensive. Therefore, the cost associated with this method is justifiable only under certain circumstances, such as when is it mandatory that the nitrogen that is to be used in a particular application be substantially pure, when the only practical way of delivering nitrogen from the production facility to the location of use is in its liquid bulk form, and/or when there is a demand for the oxygen that is simultaneously obtained in this operation.
It was already previously attempted to obtain high-purity or even substantially pure nitrogen in various ways other than ambient air liquefaction and fractionation. Thus, for instance, it has been realized that a hydrocarbon air fuel cell device produces a relatively clean nitrogen rich exhaust product. Based on this recognition, it was proposed in commonly assigned U.S. Pat. Nos. 4,767,606 and 4,792,502 to Trocciola et al to combine a fuel cell device of this type with a cryogenic liquefaction and fractionation apparatus in such a manner that such apparatus converts the fuel cell cathode exhaust gas, which contains nitrogen, oxygen and water vapor, into a substantially pure nitrogen product. However, even this process is too expensive, despite the fact that the cathode exhaust gas contains a much lower percentage of oxygen than ambient air, unless the above conditions are present.
On the other hand, it is known from a commonly assigned U.S. Pat. No. 4,751,151 to Healy et al to employ a carbon dioxide absorber in a fuel cell system to recover carbon dioxide from the fuel cell anode exhaust stream (fuel gas) containing principally hydrogen, carbon dioxide, carbon monoxide, and water vapor. However, even this process would be rather uneconomical if it were attempted to use the thus constructed system with a hydrocarbon air fuel cell device, especially since the anode exhaust stream carries only about 20% of the nitrogen passing through such fuel cell device.
Moreover, there are already known various constructions of gas purifying devices, among them such using polymer membranes and the pressure swing absorption approach, for removing unwanted gaseous ingredients from gases, such as oxygen from air, to obtain high-quality nitrogen product. However, even these processes as previously applied to the production of nitrogen from air leave much to be desired in terms of economy of operation and thus cost of the thus obtained high-purity nitrogen.
Accordingly, it is a general object of the present invention to avoid the disadvantages of the prior art.
More particularly, it is an object of the present invention to provide a method of producing high-purity nitrogen gas, which method does not possess the disadvantages of the known methods of this kind.
Still another object of the present invention is so to develop the method of the type here under consideration as to reduce the cost of the high-purity nitrogen obtained by using this method.
It is yet another object of the present invention to devise an apparatus which is suitable for the performance of the method of the above type.
A concomitant object of the present invention is design the apparatus of the above type in such a manner as to be relatively simple in construction, inexpensive to manufacture, easy to use, and yet reliable in operation.